The present, most important task of experimental population genetics is to attempt to determine exhaustively the actual allelic variation present in populations by any and all methods that will detect gene substitutions. We plan to assess the limits of resolution of the most commonly employed technique for this purpose, native gel electrophoresis. We will examine the effects of known single and multiple amino acid substitutions in the proteins bacteriophage T4 lysozyme and the alpha subunit of (Escherichia coli) tryptophan synthetase on the mobility phenotypes of these enzymes measured by currently standard electrophoresis conditions. This will allow us to partition the large number of sequenced mutants of these proteins into mobility classes indistinguishable by current electrophoresis methods and to determine exactly which kinds of substitutions can be resolved by these methods. By varying the parameters of electrophoresis, and coupling these new electrophoresis methods with attempts to further resolve mobility classes of these two proteins, we may be able to facilitate the development of more sensitive electrophoresis techniques. The end product of this study will be a measure of the correspondence between the mobility phenotype and the primary amino acid sequence of a large number of variants of these two proteins, including proteins having previously characterized missense, suppressed nonsense and frameshift-induced amino acid substitutions.